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Hydrogen Storage Capacity of Mg/Mg2Ni Eutectic Doped with Elements from Groups XIII and XIV
Čermák, Jiří ; Král, Lubomír
In the present paper, the chemical composition of Mg-8.5 at.% Ni-2.7at.%X alloys (X – elements of the 13th and 14th groups) as prospective hydrogen storage was investigated. Experimental alloys were studied in three states: (i) after stabilization anneal, (ii) after stabilization anneal and hydrogen charging, and (iii) after stabilization anneal, hydrogen charging and hydrogen desorption. It was ascertained that a ratio of concentration of X in two principal phases – Mg2NiH4(-X) and MgH2(-X) – was a decreasing function of the ionization potential of X. The stronger the preference of X for Mg2NiH4-X phase, the higher the hydrogen storage capacity of Mg-Ni-X alloy was. For X = In, the hydrogen storage capacity was slightly higher than the capacity of an un-alloyed binary eutectic Mg-Ni alloy.
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Improvement of Hydrogen Desorption Characteristics of Eutectic Mg/Mg2NiH4 and Mg2NiH4 by In addition
Čermák, Jiří ; Král, Lubomír
Mg-xNi alloys are known as perspective hydrogen storage materials [1,2]. Hydrogen storage capacity and hydrogen desorption rate of binary alloys Mg-Ni are, however, still unsatisfactory and therefore, improvements are sought, e.g., by introduction of a proper catalyst [3]. As candidate elements, transition metals [4] are often used that attract bonding valence electrons and, hence, destabilize the hydrides. However, also elements with weaker bond to H than that of Mg, or even non-hydride forming elements show a beneficial effect upon the hydrogen desorption rate [5,6]. The present investigation continues our previous work [7,8]. Here we investigate the resistance of eutectic Mg/Mg2Ni against the poisoning by residual air and possible ways how to improve the hydrogen desorption kinetics of Mg2NiH4 by doping. As dopants, elements of the 13th and the 14th group were tested that do not form stable hydrides.
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Corrosion of Nickel Exposed to LiF-NaF Molten Salt
Král, Lubomír ; Čermák, Jiří ; Matal, O. ; Šimo, T. ; Nesvadba, L.
This work is devoted to study of changes of structure and chemical composition in corrosion areas of the chosen candidate alloy, Nickel 201, for components of a LS-VHTR. The material was annealed at 1013K/10h/vacuum and at 1000°C/24h/Ar before corrosion tests. The annealed material was studied after its exposure to the molten mixture of 60 mol. % LiF + 40 mol. % NaF at the temperature of 1013K. The exposition was carried out in a quasidynamic regime, which simulates real circulation of the coolant (a mixture of molten salts) in the piping. The structure of the alloy was studied by SEM. Severe corrosion damage was observed in grain boundaries.
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Corrosion of chosen Ni-based material exposed to LiF-NaF molten salts
Král, Lubomír ; Čermák, Jiří ; Matal, O. ; Šimo, T. ; Nesvadba, L.
This work is devoted to study of changes of structure and chemical composition in the surface layer of chosen candidate alloy Ni – 6 W – 9 Mo – 1.7 Ti – 7 Cr (in wt. %) for components of a LS-VHTR. The material was studied after its exposure to molten mixture 60 mol. % LiF + 40 mol. % NaF at temperature 993 and 1013K. The exposition was carried out in a quasidynamic regime, which simulates coolant (the mixture of salts) natural circulation conditions in components. The structure of the alloy was studied by SEM. Severe corrosion damage was observed in the surface layer, which thickness was about 300 μm.
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Low-temperature diffusion of carbon in iron measured by SIMS technique
Čermák, Jiří ; Král, Lubomír
Depth profiling mode of MiniSIMS device was applied to diffusion measurement. As an example, carbon diffusion in BCC iron was studied. There are sparse experimental diffusion data at temperatures below the eutectic horizontal (996 K). This is caused by the fact that direct measurement of carbon diffusion coefficient in ferrite at low temperatures is complicated by very low solubility of carbon. For practical purposes, the extrapolation of high-temperature data to low temperature region is usually used for estimation of diffusioncontrolled kinetics in ferrite alloys. Present work has shown that the SIMS technique can be applied to the study of carbon diffusivity in iron. Special technique was developed, which avoids radio-tracer measurements with C-14. Obtained results are lower than the extrapolated values, which may be due to limited solubility of carbon in iron.
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Analýza přerozdělení prvků feritických ocelí s Ni povlakem pro technologie roztavených solí
Král, Lubomír ; Čermák, Jiří ; Matal, O. ; Šimo, T. ; Nesvadba, L. ; Jílek, M.
Changes in structure and chemical composition of Ni-coated ferritic steel ČSN 411523 are studied in the present paper. The Ni-coated material is perspective for applications in molten salts technologies. The samples were subjected to corrosion in molten mixture 60 mol. % LiF + 40 mol. % NaF at temperature 953 K, the duration exposition was 100, 300 and 1000 h. Experiments were carried out in a quasidynamic regime simulating the flow of the cooling media (the mixture of molten salts) in the pipeline system. The change of chemical composition in the vicinity of interface between the Ni layer and steel substrate was measured by SEM.
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Objemová kovová skla na bázi železa - optimalizace odlévání
Stloukal, Ivo ; Král, Lubomír ; Čermák, Jiří
In this paper, the iron-based alloy was studied that is perspective for preparation of bulk metallic glass. The nominal composition of investigated material is given by the formula Fe.sub.56./sub.Co.sub.7./sub.Zr.sub.10./sub.Mo.sub.5./sub.W.sub.2./sub. B.sub.15./sub.. Two casting techniques were applied: (i) conventional casting into a copper mould in the induction furnace and (ii) casting in the arc furnace in the copper mould. In the first case, the diameter of the ingot was about 11 mm. In the second case, the special two-parts copper moulds differing in diameters of the casting inlet hole (3 and 1 mm, respectively) were used. The microstructure of alloys prepared by both techniques was studied using the light optical microscopy, SEM (Scanning Electron Microscopy) and XRD (X-ray diffraction).
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Kinetika vodíku v Mg2Ni a v hydrogenovaném eutektiku Mg-Mg2Ni
Čermák, Jiří ; Král, Lubomír ; Stloukal, Ivo
Time dependence of total amount of hydrogen desorbed from hydrogen-charged Mg and eutectic Mg-Mg2Ni (23.5 wt. % Ni) alloy was measured at temperatures from interval 552 – 723 K. Experiments were carried out well below the equilibrium pressure, where these hydrides – perspective as solid hydrogen storage media – are unstable and the desorption process is controlled mainly by diffusion of hydrogen in respective hydride (MgH2 and/or Mg2NiH4). Hydrogen diffusion coefficients were evaluated from desorption curves and hydrogen diffusion coefficient along interphase boundary MgH2/Mg2NiH4 was estimated from results obtained with the eutectic alloy.
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Strukturní změny ve slitinách Mg-Ni po absorpci a desorpci vodíku
Král, Lubomír ; Čermák, Jiří
This paper deals with changes of structure in Mg-Ni alloys after absorption and desorption of hydrogen. Experimental materials were prepared by two techniques – by casting and by ball milling and subsequent compacting to pellets. These materials were hydrogen-charged at elevated temperature and pressure. Materials were studied using the SEM Jeol JSM 6460 equipped with EDS/WDS analyzers. Formation of rectangular particles of MgNi2, nucleation of MgH2 at grain boundaries, and changes of Mg2Ni were observed. The so-called activation of hydrogen storage alloy is most likely due to fine particles that appear after the first hydrogen charging.
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